Reactive Training Systems

You can use a third-party application like KDETools Zimbra to Outlook Converter to transfer Zimbra into Outlook.

Some features include:

• In addition to Zimbra files, this tool can transfer MBOX, MSG, EML, EMLX, PDF, HTML, and other file types.
• It extracts every necessary item of mail data, including the To, Bcc, Cc, Sent, From, Received, and Attachments, among others.
• Without losing any data, this program makes it simple to transfer Zimbra file into Outlook.

More details:  http://www.zimbra-converter.com/office-365/